In reproduction of multichannel audios, speaker arrangement on a reproduction side and sound source positions of audio signals to be reproduced are desired to be completely the same. In reality, however, the speaker arrangement on the reproduction side is not the same as the sound source positions in most cases.
There is a sound source that does not exist in positions of the speakers due to a difference between the speaker arrangement on the reproduction side and the sound source positions, and therefore how to reproduce such a sound source attracts great attention.
In order to obtain audio signals corresponding to the speaker arrangement on the reproduction side, generally, audio signals of the respective sound source positions, i.e., respective channels are mixed by using mixing equations, and audio signals of new channels corresponding to the speakers on the reproduction side are generated.
In this case, conventionally, an appropriate pattern is selected from several patterns provided in advance as a parameter in mixing equations set in advance, and mixing coefficients to be multiplied by the audio signals of the respective channels in fee mixing equations are calculated (i.e., see Non-patent Literature 1).
For example, Non-patent Literature 1 discloses that the following equations (1) are calculated as down-mixing of 22.2 channel arrangement to 5.1 channel arrangement in the standard ARIB STD-B32 version 2.2 [1] of Association of Radio Industries and Businesses (ARIB).
                    [                  Math          .                                          ⁢          1                ]                                                                      L          =                      a            ⁡                          (                              FL                +                                                      1                                          2                                                        ⁢                                      (                                          FLc                      +                      SiL                                        )                                                  +                                  k                  ⁡                                      (                                          TpFL                      +                                                                        1                                                      2                                                                          ⁢                                                  (                          TpSiL                          )                                                                    +                      BtFL                                        )                                                              )                                      ⁢                                  ⁢                  R          =                      a            ⁡                          (                              FR                +                                                      1                                          2                                                        ⁢                                      (                                          FRc                      +                      SiR                                        )                                                  +                                  k                  ⁡                                      (                                          TpFR                      +                                                                        1                                                      2                                                                          ⁢                                                  (                          TpSiR                          )                                                                    +                      BtFR                                        )                                                              )                                      ⁢                                  ⁢                  C          =                      a            ⁡                          (                              FC                +                                                      1                                          2                                                        ⁢                                      (                                          FLc                      +                      FRc                                        )                                                  +                                  k                  ⁡                                      (                                          TpFC                      +                                                                        1                                                      2                                                                          ⁢                                                  (                          TpC                          )                                                                    +                      BtFC                                        )                                                              )                                      ⁢                                  ⁢                  LS          =                      a            ⁡                          (                              BL                +                                                      1                                          2                                                        ⁢                                      (                                          SiL                      +                      BC                                        )                                                  +                                  k                  ⁡                                      (                                          TpBL                      +                                                                        1                                                      2                                                                          ⁢                                                  (                                                      TpSiL                            +                            TpBC                                                    )                                                                    +                                                                        1                          2                                                ⁢                        TpC                                                              )                                                              )                                      ⁢                                  ⁢                  RS          =                      a            ⁡                          (                              BR                +                                                      1                                          2                                                        ⁢                                      (                                          SiR                      +                      BC                                        )                                                  +                                  k                  ⁡                                      (                                          TpBR                      +                                                                        1                                                      2                                                                          ⁢                                                  (                                                      TpSiR                            +                            TpBC                                                    )                                                                    +                                                                        1                          2                                                ⁢                        TpC                                                              )                                                              )                                      ⁢                                  ⁢                  LFE          =                                    1                              2                                      ⁢                          (                                                LFE                  ⁢                                                                          ⁢                  1                                +                                  LFE                  ⁢                                                                          ⁢                  2                                            )                                      ⁢                                  ⁢                  a          =                                                    2                            3                        ·                          2              3                                      ⁢                                  ⁢                              k            =            1                    ,                      1                          2                                ,                      1            2                    ,                      1                          2              ⁢                              2                                                                        (        1        )            
In the equations (1), audio signals of channels such as FL, FR, and FC in 22.2 channel arrangement are added by using mixing coefficients to calculate audio signals of channels L, R, C, LS, RS, and LFE after down-mixing. In the equations (1), one of two values can be selected as a parameter a, and one of four values can be selected as a parameter k.
The coefficients multiplied in the equations (1) by the channels before down-mixing to obtain audio signals of the respective channels after down-mixing are mixing coefficients. For example, in the equations (1), a mixing coefficient multiplied by as FL channel to obtain as L channel is a value of the parameter a, and a mixing coefficient multiplied by an Fix channel to obtain the L channel is a/(21/2). Note that, hereinafter, a channel will also be simply referred to as “ch”.